1. Background of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning structure, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one exposure, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam of radiation in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
A lithographic apparatus may include an illumination system configured to provide a beam of radiation to a reticle. The reticle may be of a reflective or transmittive type. After the beam has been reflected or transmitted by the reticle, the beam is provided with a pattern which was present on the reticle. The so-called ‘patterned beam’ is then projected onto a target portion of a substrate by a projection system. In EUV lithography, the illumination system and the projection system include optical mirrors to process the radiation beam. In current illumination systems, a radiation attenuator may be positioned to attenuate the radiation beam such as to manipulate the positioning and size of the beam on the target portion of the reticle. In EUV lithographic apparatus, the most suitable place to arrange a radiation attenuator in an illumination system is very close to the reflective reticle. However, for example, reticle masking blades systems can be relatively large. Because of a limited space, together with the relatively large dimensions of such reticle masking blades, the design of such systems is restricted.